There is known in the art a vibration motor comprising a concentrator of longitudinal vibrations consisting of two series-arranged stages. The first stage contacts a piezoelectric cell while the second, driving, stage is fashioned as circumferentially arranged inclined rods coupled by their ends with a rotor.
Such a design is characterized by a low torque of the rotor in view of a small area of contact between the concentrator and rotor. An increase in the number of rods results in additional energy losses due to parasitic bending vibrations of said rods.
For increasing the contacting surface in vibration motors use can be made of prior art concentrator of torsional vibrations comprising two cylinder-shaped stages arranged coaxially and in series with each other. The first one of said stages has a larger cross-sectional area, contacts a piezoelectric cell and is provided with means for transforming longitudinal vibrations imparted to said stage by the piezoelectric cell into torsional vibrations. The function of the vibration transforming means is served by oblique slots provided in the first stage along the line of propagation of torsional vibrations. The second, driving, stage contacts a rotor over the entire end surface thereof.
The concentrator length l is selected in accordance with the formula EQU .lambda..sub.1 /4&lt;l=.lambda..sub.2 /2 (I)
wherein
.lambda..sub.1 is the wavelength of longitudinal vibrations in the rod, and
.lambda..sub.2 is the wavelength of torsional vibrations in the rod, or the formula EQU .lambda..sub.3 /4&lt;l=.lambda.'.sub.2 /2 (II)
wherein .lambda..sub.3 is the wavelength of radial vibrations, and
.lambda.'.sub.2 is the wavelength of torsional vibrations in a radial medium,
depending upon the specific concentrator embodiment (cf., M. G. Sirotjuk, Transformation of Acoustic Longitudinal Vibrations to Shear or Torsional Ones, Akusticheskii zhurnal-Acoustic Journal, vol. 5, No. 2, 1959, p. 254). The concentrator of the vibration motor is excited by longitudinal vibrations, however, the choice of the concentrator dimensions in accordance with Formula (I) or (II) and the provision of oblique slots result in the shaping of torsional vibrations. As a result, the driving stage surface is oscillated by longitudinal-torsional or radial-torsional vibrations whose energy sets to rotation the rotor contacting the concentrator.
The torque on the shaft of a vibration motor provided with such concentrator is higher as compared to a vibration motor the driving stage of whose concentrator is fashioned as inclined rods, owing to an increased area of contact of the concentrator driving stage with the rotor. However, the power of such vibration motor is inadequate in view of a low value of the coefficient of vibration displacement concentration and, as a result, of a low amplitude of torsional vibrations at the concentrator outlet.